1. Field of the Invention
This invention relates to improved zinc silicate particles and a method of forming such particles. More particularly this invention relates to an improved method of formation of such particles from silicic acid, and to the improved particles produced by the method.
2. Discussion of References
U.S. Pat. No. 2,656,320 of Nagy et al for "Zinc Silicate Phosphor", combines silicic acid and zinc oxide with magnesium (nitrate, carbonate or hydroxide) as an activator. The purpose is to form an orthosilicate as opposed to a metasilicate. Manganese is added (preferably nitrate) and the resulting material is ball-milled wet for one hour at 130.degree. C. until dehydrated or ball-milled dry for two hours and then heated at 1240.degree. C. for one hour. The product is screened through a 100-mesh screen and refired for one to three hours at 1240.degree. C. Alternatives to magnesium nitrate, as the activator, are zirconium oxide or the combination of magnesium and zirconium oxides.
U.S. Pat. No. 2,845,564 of Herold for "Cathodoluminescent Phosphors and Devices" describes preparation of luminescent material from magnesium oxide (as the oxide), cadmium oxide (as the carbonate), zinc oxide (as the oxide), silicon dioxide (as silicic acid), manganese (as the sulfate) and flux (as cadmium chloride). The material is ball-milled with water for four to twelve hours, dried and then fired at 1050.degree. C. in air for four hours. The composition of the product is 5MgO.2CdO.ZnO.7SiO.sub.2 :0.04 Mn. Manganese is employed as an activator.
U.S. Pat. No. 3,766,084 of Malarkey for "Method of Preparing an Ultraviolet Emitting Phosphor" employs silicic acid, SrCO.sub.3, SrF.sub.2, ZnO, and PbO, ball-milled in dry powder form for fifteen to twenty hours, or wet milled for two hours after adding acetone. The dry product, after milling, is fired at 1275.degree. to 1325.degree. C.
U.S. Pat. No. 2,274,272 of Leverenz for "Luminescent Material" describes preparation of a luminescent material by precipitating beryllium carbonate, zinc carbonate, and manganese carbonate from a nitrate solution of those metals by adding ammonium carbonate. The mixed material is then precipitated onto very finely divided SiO.sub.2 particles, which can be in a colloidal suspension. The mixture is dried and heated to 700.degree. to 1600.degree. C. with an optimum value of 1150.degree. C. A temperature of 1200.degree. C. is mentioned in an example. The phosphor produced is a 40% Be, 60% Zn phosphor. The zinc is added before the ammonium carbonate is added and before the precipitation of the solution onto the particles of silica.
U.S. Pat. No. 2,314,699 of Hale for "Luminescent Material" describes use of zinc oxide, dispersed in a silicate solution precipitating the silica on the zinc oxide and filtering out the zinc oxide particles with their precipitated silica coating. The filtered particles are suspended in a dilute solution of manganese nitrate. The manganese may then be precipitated on the silica layer in the form of carbonate, sulfide, oxalate, oxide or phosphate. Manganese can be precipitated as carbonate by adding ammonium carbonate, or ammonium hydroxide.
U.S. Pat. No. 2,110,162 of Leverenz for "Luminescent Material" describes use of zinc nitrate and copper nitrate which are warmed and mixed together (magnesium can be substituted for the zinc); silica particles less than 100 micrometers in diameter are obtained by ball-milling or grinding and passing the material through a 400-mesh screen. Alternatively, colloidal SiO.sub.2 can be used instead of the powdered SiO.sub.2. The Zn and Cu are precipitated as carbonates, oxalates, sulfides, hydroxides or phosphates by adding ammonium carbonate or carbamate, or by adding ammonium hydroxide plus saturation with carbon dioxide. The ammonium nitrate is removed by elutriation or washing. The material is dried and then heated to 900.degree. to 2800.degree. C., 5 to 150 minutes.
Additional U.S. Patents include:
Yocom et al. U.S. Pat. No. 3,208,950 PA1 Glemze et al. U.S. Pat. No. 3,541,019 PA1 Froelich U.S. Pat. No. 2,597,631 PA1 Leverenz U.S. Pat. No. 2,457,054 PA1 Moore U.S. Pat. No. 2,238,026 PA1 Batchelor U.S. Pat. No. 2,124,225 PA1 Leverenz U.S. Pat. No. 2,306,270 PA1 ZnO: 2 moles PA1 SiO.sub.2 : 1.60-1.65 moles PA1 MgO: 0-0.11 moles PA1 MnO: 0.006-0.014 moles PA1 As.sub.2 O.sub.3 : 285-1120 parts per million; PA1 ZnO: 2 moles PA1 SiO.sub.2 : 1.1-1.75 moles PA1 MgO: 0-0.11 moles PA1 MnO: 0.0025-0.02 moles PA1 As.sub.2 O.sub.3 : 0-2000 parts per million; PA1 ZnO: 1 PA1 SiO.sub.2 : 0.55 to 0.875 PA1 MgO: 0 to 0.06 PA1 MnO: 0.001 to 0.01 PA1 As.sub.2 O.sub.3 : 0-2000 parts per million; PA1 ZnO: 1 PA1 SiO.sub.2 : 0.8-0.83 PA1 MgO: 0-0.06 PA1 MnO: 0.003 to 0.007 PA1 As.sub.2 O.sub.3 : 285-1120 parts per million. PA1 (a) providing particles of silicic acid within a predetermined size range; PA1 (b) mixing the silicic acid particles in an aqueous solution of Mn, Mg and As cations and anions selected from the group consisting of NO.sub.3, SO.sub.4, OH, and Cl, PA1 (c) adding zinc containing particles, drying, and PA1 (d) firing the product of step (c) whereby a reacted oxide product is produced. PA1 (a) providing particles of silicic acid to sizes on the order of 1 micrometer and larger; PA1 (b) mixing the silicic acid particles in an aqueous solution of Mn, Mg and As cations and highly active anions, PA1 (c) adding zinc oxide particles to the result of step (b), drying, and PA1 (d) firing the product of step (c), whereby a reacted oxide product is produced.